Topic 8 – Lesson 2

• Workings of a generator

• Energy sources

• Renewable and non-renewable

• Energy density

Electromagnetic induction

Electromagnetic induction

If a magnet is moved inside a coil an electric current is induced (produced)

Electromagnetic induction

A electric current is induced because the magnetic field around the coil is changing.

Generator/dynamo

A generator works in this way by rotating a coil in a magnetic field (or rotating a magnet in a coil)

Energy Sources

Non-renewable?

Non-renewable

• Finite (being depleted – will run out)

• In general from a form of potential energy released by human action

Fossil fuels – Coal, oil, gas

Nuclear fuels

Renewable?

Renewable

• Mostly directly or indirectly linked with the sun

• The exception is tidal energy

Photovoltaic cells

Active solar devices

Wind

Wave

Tidal

Biomass

World energy production

Fuel % total energy production

CO2 emission g.MJ-1

Oil 40 70

Natural gas 23 50

Coal 23 90

Nuclear 7 -

Hydroelectric 7 -

Others < 1 -

Energy Density

Energy Density

• The energy that can be obtained from a unit mass of the fuel

• J.kg-1

• If the fuel is burnt the energy density is simply the heat of combustion

Energy density

• Coal - 30 MJ.kg-1

• Wood - 16 MJ.kg-1

• Gasoline – 47 MJ.kg-1

• Uranium – 7 x 104 GJ.kg-1 (70000000 MJ.kg-1)

Hydroelectric energy density?

Hydroelectric energy density?

• Imagine 1 kg falling 100m.

• Energy loss = mgh = 1x10x100 = 103 J

• If all of this is turned into electrical energy it gives an “energy density” of the “fuel” of 103 J.kg-1